<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>边距内圆角</title>
    <style>
        .rad {
            background: tan;
            border-radius: .8em;
            padding: 1em;
            box-shadow: 0 0 0 .6em #655;
            outline: .6em solid #655;
        }
    </style>
</head>

<body>
    <div class="rad"></div>
</body>

</html>